Various lithography or surface patterning techniques have been demonstrated to fabricate well-defined structures at the nano and micro scale [1-2]. Such techniques, which are also referred to as nano/microfabrication, are critical for both academic researches and industrial applications in different areas such as electronics, optics, sensors and medical sciences [3-9]. One challenge for applying the various lithographic techniques in nano/microfabrication is the simultaneous control of costs, throughput, resolution, and pattern flexibility. Generally, the lithographic techniques can be divided into two strategies: the mask-based and the maskless lithography. The mask-based methods which may include, for example, photolithography, micro-contact printing [10] and nanoimprinting [11], are straight forward methods and are capable for high-throughput and large-area patterning. These methods rely on the pre-designed mask, through which the patterns are transferred from the mask to the substrate. Hence, these mask-based methods are not suitable to fabricate arbitrary structures [12]. In this regard, the maskless lithography, for example, electron-beam lithography, direct laser writing, ion-beam lithography, and scanning probe-based lithography methods are good alternatives to directly write arbitrary well-defined structures both at nano and micro scale. Among the scanning probe lithographic methods, cantilever-based scanning probe lithography such as dip-pen nanolithgraphy (DPN) [13], is a promising method to directly write arbitrary well-defined structures both in nano and micro scale [14-18]. However, single-cantilever DPN suffers from low throughput, and parallel DPN [19-21] requires highly specialized and expensive cantilever array [22]. Aimed to provide a low-cost cantilever-based scanning probe lithographic method, “Dip-Pen” Nanolithography (DPN) has been demonstrated in a variety of applications in patterning a number of molecules onto a surface at different length scale, see PCT International application number: WO/2009/143378, WO/2008/121137, WO/2008/020851, WO/2003/052514, and WO/2001/091855. The DPN method can be readily scale up by applying a 1D or 2D cantilever array despite that the cost increases.
Recently, a very promising method which combines the low-cost and large-area patterning advantages of micro-contact printing with the maskless property of DPN, namely the polymer pen lithography (PPL) has been demonstrated, see PCT International application number: WO/2009/132321, WO/2010/096591, and WO/2010/124210. The PPL has been invented for patterning arbitrary structures of molecular-based materials, such as thiol SAM, polymer and nanoparticles. This method comprises a pyramid-shaped array of h-PDMS tips or agarose tips mounted onto a glass slide, through which the pre-soaked ink molecules are delivered onto the substrate. The PPL method well addresses the challenges in the throughput of large-area patterning with maskless patterning methods without increasing the cost. However, there are two drawbacks in PPL: (1) the optical leveling techniques cannot solve 0.02° difference in angle between the planes defined by the tip array and the substrate, and this imprecise leveling will result in great variation of feature size written by different polymer pens across the substrate; (2) since the Young's modulus of the tip materials is very low, tip deformation is very sensitive to the z-piezo extension, and thus it is difficult to control the feature size and it is not feasible to fabricate patterns with small increment in size. In order to address the leveling issue, instead of monitoring the tip deformation, a more precise but specialized leveling method based on the force-feedback system has been introduced. In that method, by placing a scale beneath the substrate surface, as small as 0.004° difference in angle between the planes defined by the tip array and the substrate can be achieved. Nevertheless, this force-feedback system needs a very sensitive scale fixed on the stage and the leveling process is relatively complicated, which may not be convenient for ordinary laboratories. In order to address the large feature sensitivity of z-piezo extension, a hard-tip soft-spring lithography method (HSL) has been introduced, see PCT International application number: WO/2010/141836. In the HSL method, the h-PDMS tips in PPL are replaced by an array of silicon tips mounted onto an elastomeric layer. Although the HSL allows great improvement on the leveling feasibility and patterning resolution, this method suppresses the force dependent property of PPL. Moreover, the fabrication of HSL is very complicated and therefore the costs is relatively high, especially when a specially made silicon wafer of 50 μm thick with SiO2 layers of 1 μm thick on each side of the wafer is required to fabricate the tips array.
It is an object of the present invention to overcome or mitigate at least one of the aforesaid disadvantages of the prior art, or to provide a useful alternative to the prior art.